when you have a wand in your main hand and a broomstick in you off hand. The moment when you active the broomstick your wand will be removed and when you dismount it you get a broomstick but not your wand. The broomstick in your off hand still be there.

Eek, thanks for the report- I'll try and fix that ASAP.

This is fixed in 6.9.2 (latest dev build)- thanks!